The objective of this program project is to evaluate the role of dietary selenium (Se) in cancer. Both human subjects and experimental animal systems will be studied. The human-based study will measure the correlational relationship between Se nutritional status and various cancers in selected areas of the Peoples Republic of China where it is known that human intake of Se is extraordinarily variable. Se nutritional status will be evaluated through estimation of Se intake (corrected for bioavailability) and measurement of hair Se (a method of proven value in previous Se studies in China). Nutritional status and intakes for two other groups of nutrients will also be evaluated; one group will be those which are known to interact with Se (vitamin E, vitamin A/Beta-carotene, vitamin C, and vegetable fat) whereas the second group of nutrients will be studied because of their alleged independent association with some cancers (protein, fat, dietary fiber, zinc, riboflavin and cholesterol). This study will permit an assessment of both an independent contribution of Se as well as a comparison of its effects with certain other nutrients of interest. The human-based studies will be supplemented with experimental studies undertaken at Cornell University to examine in more depth the role of Se in experimental carcinogenesis. Special emphasis will be given to a) the role of dietary fat in Se activity, b) the role of Se in azaserine-induced pancreatic cancer and aflatoxin-indueced hepatocarcinogenesis, c) the combined roles of Se and fat in the more general aspects of the post-initiation phase of experimental carcinogenesis, d) the physico-chemical properties of dietary fiber as related to Se absorption and e) the factors affecting Se bioavailability. Immune completence and nutritional status of selected animals used in these studies will be established. During the first two years of this project, colleagues in Finland will consult with the investigators of this program project because of an on-going Se intervention trial which should provide a later opportunity for examination of the role of Se in prostaglandin metabolism and activity in humans. The results of this program project should provide reasonably definitive information on the alleged role for Se in human and experimental carcinogenesis.